1. Field
The present invention relates generally to the field of regrown bipolar transistors, and more particularly to regrown heterojunction bipolar transistors (HBT) for multi-function integrated circuits and method for fabricating the same.
2. Description of the Related Art
Compared to conventional silicon-based homojunction bipolar junction transistors (BJT), a heterojunction bipolar transistor (HBT) may have an emitter layer with a larger bandgap and a base layer with a smaller bandgap. The larger bandgap emitter layer may provide a better barrier for hole injection, which may be initiated from the base layer. Accordingly, the base layer may be doped at a higher doping level, thereby lowering the base resistance and improving the radio frequency (RF) performance of the HBT.
For conventional silicon-based homojunction BJT, the collector doping may be performed by an ion implantation process, which may allow the collector layers of various BJT devices to be formed on a single substrate and have different doping profiles. Attempts have been made in the past to adopt the ion implantation process for performing the collector doping of the compound semiconductor HBT devices in the Indium Phosphide and Gallium Arsenide material systems. However, due to various technical issues, the ion implantation process is generally not used for collector doping of these compound semiconductor HBT devices.
Accordingly, the collector doping of HBT devices may be performed by an epitaxial growth process. Currently, the epitaxial growth process may allow growing HBT devices with a single collector doping profile on a single substrate. In order to develop HBT devices with multiple collector doping profiles, at least two substrates may be needed. However, multiple substrates may lead to additional parasitic effects and inter-chip routing. As such, it may become inefficient for multi-function integrated devices to have multiple HBT devices with different collector doping profiles.
Thus, there is a need to provide a single chip solution to grow and regrow multiple HBT devices for multi-function integrated devices.